Can I change the default time of push notifications?

Hope I'm asking the right question. I have three e-mail accounts, a Twitter and Facebook. I have no idea how often the Blackberry OS scans (pushes?) to check for new e-mails and notifications, but I get the feeling its more than once an hour.

Where can I access these settings so that I can configure the phone to say, check everything once every two or three hours, or manually by me when I want?

Or can I configure it further to check each account in a different time frame e.g.

Thank you very much. With that info I found my e-mail account settings and they were all set to 30-minute intervals. I've now changed them all, very helpful, and I hope this saves a bit of battery life (I don't think I'm doing brilliantly on this front).

Another question if I may; what's the difference between Sync Interval and Sync Timeframe? The latter has much longer er... timeframes, but its not obvious what the difference between the two is.